Even if taking the RV means driving CA-1 more slowly than you would in a car, it makes far more sense to me to take the RV earlier and use it to go to Monterey, then going to Sonora from there. Frankly, the back-tracking to SF just to return the car and switch to Rv seems like a great waste of time.
RVs drive CA-1 all the time. Just keep these things in mind and you'll be fine. Drive at a slow, easy pace so that the RV navigates the curves easily. Pull over anytime you have more than 5 cars behind you to allow them to pass you. Know that the trip is going to take a bit longer but you're going to see amazing views so just relax and enjoy it.
Anyway, that's what I'd do. I think with the limited vacation days you have for your trip, it's the best use of your time.